The present invention relates to an alternating-current generating apparatus for an automotive vehicle comprising an alternator which is driven by an internal combustion engine via a one-way clutch.
Conventionally, from the view point of global environmental protection, reduction of emission gas and reduction of fuel consumption are essential targets to be attained. When driving, automotive vehicles are often in idling conditions where the engine does not contribute to drive. In view of the above, there is a tendency that the engine rotational speed in this idling condition (hereinafter referred to as idling speed) is set to a relatively low value. However, reducing the idling speed will encounter with the difficulty in stabilizing the engine rotation due to increase of friction. This problem is remarkable in the diesel engines. Furthermore, long-term cyclic fluctuation of the engine rotation will appear due to delay caused in the control system of the internal combustion engine.
The low idling speed condition causing undesirable fluctuation in the engine rotation may be referred to as an idle hunting state. FIG. 4 shows the behavior of the automotive alternator in such a low idling speed condition.
It is now assumed that, in the idle hunting state, the engine rotational speed is decreasing. In this case, the rotational speed of the automotive alternator reduces correspondingly with reducing engine speed. However, under a condition that the automotive alternator is working for a constant electric load, a required driving torque of the automotive alternator increases with reducing engine speed. As a result, the increased driving torque of the automotive alternator will undesirably promote the reduction of the engine speed. On the contrary, when the engine speed is increasing, the required driving torque of the automotive alternator decreases with increasing engine speed. As a result, the decreased driving torque of the automotive alternator will undesirably promote the increase of the engine speed.
To solve the above-described troublesome hunting promotion appearing in the engine rotational speed of this kind of automotive alternator, the published Japanese patent No. 7-72585 discloses a one-way clutch disposed in a driving pulley of the alternator. The one-way clutch equipped pulley operates in the following manner.
When the rotational speed of the internal combustion engine is decreasing (i.e., in a deceleration condition), large-small relationship between an inertia torque of the alternator and an output torque generated from the engine torque is inversed momentarily. In this case, the one-way clutch is brought into a disengaged state so that the degree of engine speed reduction can be suppressed. The undesirable fluctuation of engine rotation can be suppressed correspondingly.
However, the research and tests conducted by the inventor of this application have revealed that the above-described one-way clutch equipped pulley does not bring satisfactory effects in the suppression of engine rotational fluctuation appearing in the automotive alternator.
Hereinafter, the problem of the one-way clutch equipped automotive alternator will be explained in more detail with reference to FIG. 7.
An external wheel 33 of a one-way clutch is entrained by a crank pulley (not shown) via a belt. A clutch portion, comprising sprag and roller members and a spring member (which are not shown), selectively engages or disengages an internal wheel 31 and the external wheel 33.
A driving torque xcfx841 of the internal combustion engine acts on the external wheel 33. A driving torque xcfx842 of the automotive alternator, which is referred to as power generation torque, acts on the internal wheel 31 in a direction opposed to the engine driving torque xcfx841. Furthermore, inertial of an alternator rotor causes an inertial torque xcfx843 which also acts on the internal wheel 31. The inertial torque xcfx843 changes its direction in accordance with change of rotation of the internal wheel 31. The direction of the inertial torque xcfx843 is identical with that of the alternator driving torque xcfx842 when the rotational speed of the internal wheel 31 is increasing and is opposed when decreasing. Engagement and disengagement of the one-way clutch is designed so as to be determined according to the large and small relationship among these three torques.
The directions of torques xcfx841, xcfx842, and xcfx843 shown in FIG. 7 are now assumed to be positive, while xcfx891 represents the rotational speed of the internal wheel 31 and xcfx892 represents the rotational speed of the external wheel 33. The one-way clutch is engaged when xcfx841xe2x89xa7xcfx843xe2x88x92xcfx842 (where xcfx891=xcfx892) and is disengaged when xcfx841 less than xcfx843xe2x88x92xcfx842.
At a moment the engine speed starts decreasing from accelerating or constant speed rotation, the torque xcfx841 decreases correspondingly. In this case, the inertial torque xcfx843 of the automotive alternator will exceed the engine driving torques xcfx841 which acts in the same direction as that of the inertial torque xcfx843. The above condition xcfx841 less than xcfx843xe2x88x92xcfx842 is established. Thus, the one-way clutch is disengaged.
Subsequently, the rotational speed of the automotive alternator decreases due to power generation torque xcfx842 as well as friction loss at the bearing portion and wind loss at the cooling fan.
When the rotational speed of the automotive alternator starts decreasing, the above-described power generation torque xcfx842 increases correspondingly. This will forcibly and promptly decrease the rotational speed of the alternator. The composite torque acting on the internal wheel 31 will soon be equalized with the torque acting on the external wheel 33. Thus, the one-way clutch is engaged shortly.
According to recent compact high power automotive alternators, the power generation torque xcfx842 is larger than the inertia torque xcfx843 during the disengaged state of the one-way clutch. Therefore, the rotational speed of the alternator rotor decreases quickly and the one-way clutch is again engaged within a short period of time after the one-way clutch is once disengaged, even when the engine speed is decreasing or in the very beginning of acceleration from its lowest rotational speed (where the increasing rate of the rotational speed is small).
As a result, the above-described conventional automotive alternator cannot bring satisfactory effect, although the one-way clutch is intentionally provided to release the internal combustion engine from the load torque of the automotive alternator when the internal combustion engine is decreasing.
Increasing the inertia mass of the automotive alternator is effective to solve the above-described problem since the rotational speed of the automotive alternator will not decrease so quickly. However, increased size and weight of the automotive alternator will induce another problem to be solved.
In view of the foregoing problems of the prior art, the present invention has an object to provide an alternating-current generating apparatus for an automotive vehicle which is capable of adequately suppressing the fluctuation of engine speed without increasing the size and weight of a one-way clutch equipped automotive alternator installed on an internal combustion engine.
To accomplish the above and other related objects, the present invention provides an alternating-current generating apparatus for an automotive vehicle comprising a one-way clutch, an automotive alternator driven by an internal combustion engine via the one-way clutch, and control means for controlling a power generation amount of the automotive alternator. A detecting means is provided for detecting a rotational speed of either the internal combustion engine or the automotive alternator as well as an electric amount relating to a on-off state of the one-way clutch. The control means performs at least one of two power controls when the internal combustion engine is in a low-rotational operating condition. One of the two power controls is to increase the power generation amount during an engaged state of the one-way clutch, and the other of the two power controls is to decrease the power generation amount during a disengaged state of the one-way clutch.
According to this arrangement, without increasing the size and weight of the automotive alternator, it becomes possible to prevent the rotational speed of the automotive alternator from rapidly decreasing during a disengaged state of the one-way clutch. Thus, it becomes possible to adequately suppress the fluctuation of engine rotation when the one-way clutch equipped automotive alternator is installed on an internal combustion engine.
In other words, the present invention solves the following problems.
Namely, during the disengaged state of the one-way clutch, the rotational speed of the automotive alternator, i.e., the rotational speed of the internal wheel of the clutch, decreases due to the power generation torque. As a result, even when the internal combustion engine is decelerating or in the very beginning of acceleration, the one-way clutch is re-engaged so as to increase the load torque of the internal combustion engine. This will induce undesirable reduction of rotational speed during the deceleration period of the internal combustion engine and will obstruct the buildup of acceleration in the very beginning of the acceleration period or in a situation where the acceleration rate is small. Hence, the internal combustion engine suffers from large fluctuation appearing in the rotational speed. Such undesirable fluctuation of engine speed gives adverse influence to the engine control.
However, according to the present invention, the field of the alternator can be controlled in accordance with the engaged/disengaged state of the clutch so that the engine can be maintained in adequate conditions for the control.
According to the alternating-current generating apparatus for an automotive vehicle of the present invention, it is preferable that the one-way clutch comprises a power input section for receiving a driving power from the internal combustion engine and a power output section mechanically connected to a rotor of the automotive alternator which has a plurality of filed poles. The detecting means detects a rotational speed of the power output section based on a frequency component of an output voltage of a multiphase armature winding of the automotive alternator. And, the control means compares the rotational speed of the power output section with a rotational speed of the power input section and judges that the one-way clutch is in the engaged state when the rotational speed of the power output section is equal to the rotational speed of the power input section and judges that the one-way clutch is in the disengaged state when the rotational speed of the power output section is not equal to the rotational speed of the power input section.
This arrangement makes it possible to discriminate the engaged state and the disengaged state of the clutch by using a simple comparing circuit and well-known F-V convertors.
According to the alternating-current generating apparatus for an automotive vehicle of the present invention, it is preferable that the one-way clutch comprises an external wheel portion constituting the power input section, an internal wheel portion disposed coaxially with the external wheel portion and constituting the power output section, and a clutch portion selectively engaging or disengaging the external wheel portion and the internal wheel portion.
This arrangement makes it possible to easily receive the driving power of the internal combustion engine by forming a pulley or gear portion on an outer periphery of the external wheel portion, thereby realizing an extremely compact clutch device for the automotive alternator.
According to the alternating-current generating apparatus for an automotive vehicle of the present invention, it is preferable that the automotive alternator has a field winding, and the control means is associated with switching means connected in series with the field winding for on-off controlling power current supply to the field winding. The control means closes the switching means when the one-way clutch is in the engaged state and opens the switching means when the one-way clutch is in the disengaged state.
This arrangement makes it possible to surely realize desired operations. More specifically, when the one-way clutch is in the engaged condition, the exciting current of the filed winding is increased so as to increase the electric power generation torque, thereby suppressing the rotational speed of the internal combustion from rapidly increasing. When the one-way clutch is in the disengaged condition, the exciting current of the filed winding is decreased so as to decrease the electric power generation torque, thereby suppressing the rotational speed of the internal combustion from rapidly decreasing.
It is preferable that an electric signal discriminating the engaged state and the disengaged state of the one-way clutch serves as an on/off signal of the switching means which controls the supply of the exciting current. This makes it possible to surely synchronize the engagement/disengagement of the one-way clutch with the on/off operation of the switching means. Thus, it becomes possible to instantly suppress the fluctuation of engine speed having an extremely high frequency responsive to the torque variation caused in each stroke of the internal combustion engine, thereby facilitating the engine control and suppressing the vibration.